Interpretive Summary: The soil-inhabiting fungus Verticillium dahliae causes a wilt disease resulting in severe economic losses each year in many vegetable, field and tree crops. A beneficial fungus, Talaromyces flavus, reduces losses to Verticillium wilt. This work was undertaken to determine how T. flavus provides control. Previous studies provided circumstantial evidence that an enzyme (glucose oxidase) from T. flavus resulted in production of hydrogen peroxide and that the peroxide kills the resting structures of the pathogen. In the current study, an antibody against glucose oxidase was made. The antibody was highly specific for glucose oxidase from T. flavus and did not react with other proteins from T. flavus, or with proteins from other microbes. When the antibody was used to remove glucose oxidase from culture filtrates of T. flavus, biocontrol activity was lost. When glucose oxidase was added back, biocontrol activity was restored. In the future, the antibody will be used to study the role of glucose oxidase on roots an in soil. This information will be used by scientists seeking to improve biological control to provide nonchemical alternatives for pest control.

Technical Abstract:
Culture filtrates from Talaromyces flavus grown on glucose contained high levels of glucose oxidase activity while culture filtrates from T. flavus grown on xylan contained negligible glucose oxidase activity. Culture filtrates from T. flavus grown on both media contained complex protein profiles. However, only culture filtrates from T. flavus grown on glucose inhibited germination of microsclerotia of Verticillium dahliae with in vitro inhibition assays. A polyclonal antiserum preparation, pABGO-1, raised against purified glucose oxidase from T. flavus was highly specific for glucose oxidase. Only one protein band in culture filtrates (from glucose medium), migrated at 71 kDa, was detected in Western blots. This band comigrated with purified glucose oxidase. No bands were detected in culture filtrates from the xylan medium. The glucose oxidase specific antibodies removed glucose oxidase, via immunoprecipitation, from culture filtrates of T. flavus grown in glucose medium resulting in filtrates whic no longer inhibited in vitro microscelrotial germination. When glucose oxidase depleted filtrates were amended with purified glucose oxidase from T. flavus, the ability to kill microsclerotia in vitro was restored to original levels. We conclude glucose oxidase is the only protein in culture filtrates of T. flavus responsible for inhibition of germination of microsclerotia of V. dahliae.